the way you aquire the longsword Pale Justice +4 does not make any sense. There is no way, other than coincidence, to aquire it.
In the Enhanced Edition you need to complete the quest to free Durdel Anatha's soul and then go back to the Artisan District of Lower Dorn's Deep. There are some houses where two Umber Hulks break through. This opens a passage and behind one of those houses where you can find a corpse carrying the sword.
There is no indicator during the quest of Durdel Anatha that the sword is hidden there. So why is the completion of that quest a required to trigger that event? Both seem completely unrelated. If you completed the Artisan District before completing Durdel Anatha's quest you would have no reason at all to go back there.
In my opinion there are three solutions to this:
1. Durdel Anatha was a paladin and Pale Justice is a weapon only paladins can wield. So it would make sense if he just drops it, so you can loot it from his corpse along with his remains after freeing him.
2. Make the triggering of the event unrelated to the completion of the quest. The sword is not mentioned anywhere so it would make sense to just disconnect the quest from the event. To my understanding this is how it has been in the original game. Why has it been changed in the Enhanced Edition?
3. A last option would be to just give the player hints or make its aquisition another quest. Just some way to let the player know about it. Perhaps Durdel could give those hints to connect it somehow to his quest.
It is a very powerful weapon and every player with a paladin in the group will want it. It does not make sense to hide it like that.